Oligocarbonate polyols are important precursor products in the context, for example, of the preparation of plastics, coating materials and adhesives. They are reacted, for example, with isocyanates, epoxides, (cyclic) esters, acids or acid anhydrides (DE-A 1 955 902). They can in principle be prepared from aliphatic polyols by reaction with phosgene (e.g. DE-A 1 595 446), bis-chlorocarbonic esters (e.g. DE-A 857 948), diaryl carbonates (e.g. DE-A 1 01 2557), cyclic carbonates (e.g. DE-A 2 523 352) or dialkyl carbonates (e.g. WO 2003/2630).
The oligocarbonate polyols described in the prior art and having a number-average molecular weight (Mn) of 500 to 5 000 g/mol are characterized in that they are present at room temperature (23° C.) in the solid aggregate state or else in a viscous, liquid aggregate state. The viscosity range of oligocarbonate polyols which are liquid at room temperature extends, depending on composition and number-average molecular weight, from 2 500 mPas to 150 000 mPas. Viscosities of <3 500 mPas are achieved alone by oligocarbonate polyols which often, as well as carbonate structures, contain ester units and/or have number-average molecular weights ≦1 000 g/mol. In the case of the presence of ester units, however, this results in an adverse effect, in the case for example of polyurethane systems based on so-called polyester carbonate polyols of this kind, on the stability to hydrolysis, in comparison to systems based on pure oligocarbonate polyols. Similar considerations apply to the case where ether-containing oligocarbonate polyols are used, in relation to the poorer UV resistance in relation to systems of the kind based on pure oligocarbonate polyols.
A further means of preparing pure oligocarbonate polyols of low viscosity is to use hydroxyalkyl-terminated silicones. The preparation in principle of such oligocarbonate diols which have exclusively hydroxyalkyl-terminated silicone compounds as their diol component are already known and described in Chem. Ber. (1966), 99 (2), 1368-1383. In the case of the preparation specified there, however, by means of phosgenation, there is no discernible indication that the oligomers or polymers obtained contain exclusively hydroxy-functional end groups. It is apparent, further, that oligocarbonate diols of this kind, based solely on the basis of hydroxyalkyl-terminated silicone compounds, are unsuited to the production of polyurethane coatings, since to a high degree they exhibit incompatibilities with (poly)isocyanates.
Moreover, EP-A 1 035 153, for example, teaches the preparation of polysiloxanes modified with polyester polyols and containing carbonate groups. These are hydroxyalkyl-terminated silicones which have been reacted with polyester polyols and organic carbonic esters to give copolymers. Copolymers of this kind, of whose viscosities no further details have been given, have a similarly negative hydrolysis stability behavior, owing to the presence of ester groups, as the polyester carbonate polyols described earlier on above, and so these copolymers generally find use only as additives in coatings. There is no description concerning carbonates which are free of carboxylic ester groups.
It was an object of the present invention, therefore, to provide oligocarbonate polyols which have a viscosity at room temperature (23° C.), measured in accordance with DIN EN ISO 3219, and as a function of a number-average molecular weight of between 500 and 10 000 g/mol, of less than 15 000 mPas and which do not exhibit the disadvantages recited above.